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Article
Publication date: 4 November 2014

Mica Grujicic, Ramin Yavari, Jennifer Snipes, S. Ramaswami and Roshdy Barsoum

The purpose of this paper is to study the mechanical response of polyurea, soda-lime glass (glass, for short), polyurea/glass/polyurea and glass/polyurea/glass sandwich…

Abstract

Purpose

The purpose of this paper is to study the mechanical response of polyurea, soda-lime glass (glass, for short), polyurea/glass/polyurea and glass/polyurea/glass sandwich structures under dynamic-loading conditions involving propagation of planar longitudinal shockwaves.

Design/methodology/approach

The problem of shockwave generation, propagation and interaction with material boundaries is investigated using non-equilibrium molecular dynamics. The results obtained are used to construct basic shock Hugoniot relationships associated with the propagation of shockwaves through a homogeneous material (polyurea or glass, in the present case). The fidelity of these relations is established by comparing them with their experimental counterparts, and the observed differences are rationalized in terms of the microstructural changes experienced by the shockwave-swept material. The relationships are subsequently used to predict the outcome of the interactions of shockwaves with polyurea/glass or glass/polyurea material boundaries. Molecular-level simulations are next used to directly analyze the same shockwave/material-boundary interactions.

Findings

The molecular-level simulations suggested, and the subsequent detailed microstructural analyses confirmed, the formation of topologically altered interfacial regions, i.e. polyurea/glass and glass/polyurea interphases.

Originality/value

To the authors’ knowledge, the present work is a first attempt to analyze, using molecular-level simulation methods, the interaction of shockwaves with material boundaries.

Details

Multidiscipline Modeling in Materials and Structures, vol. 10 no. 4
Type: Research Article
ISSN: 1573-6105

Keywords

Article
Publication date: 30 June 2020

Kaili Yao, Dongyang Chu, Ting Li, Zhanli Liu, Bao-Hua Guo, Jun Xu and Zhuo Zhuang

The purpose of this paper is to calculate the Hugoniot relations of polyurea; also to investigate the atomic-scale energy change, the related chain conformation evolution…

Abstract

Purpose

The purpose of this paper is to calculate the Hugoniot relations of polyurea; also to investigate the atomic-scale energy change, the related chain conformation evolution and the hydrogen bond dissociation of polyurea under high-speed shock.

Design/methodology/approach

The atomic-scale simulations are achieved by molecular dynamics (MD). Both non-equilibrium MD and multi-scale shock technique are used to simulate the high-speed shock. The energy dissipation is theoretically derived by the thermodynamic and the Hugoniot relations. The distributions of bond length, angle and dihedral angle are used to characterize the chain conformation evolution. The hydrogen bonds are determined by a geometrical criterion.

Findings

The Hugoniot relations calculated are in good agreement with the experimental data. It is found that under the same impact pressure, polyurea with lower hard segment content has higher energy dissipation during the shock-release process. The primary energy dissipation way is the heat dissipation caused by the increase of kinetic energy. Unlike tensile simulation, the molecular potential increment is mainly divided into the increments of the bond energy, angle energy and dihedral angle energy under shock loading and is mostly stored in the soft segments. The hydrogen bond potential increment only accounts for about 1% of the internal energy increment under high-speed shock.

Originality/value

The simulation results are meaningful for understanding and evaluating the energy dissipation mechanism of polyurea under shock loading, and could provide a reference for material design.

Details

Engineering Computations, vol. 38 no. 3
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 15 November 2011

M. Grujicic, W.C. Bell, B. Pandurangan, C.‐F. Yen and B.A. Cheeseman

Propagation of planar (i.e. one directional), longitudinal (i.e. uniaxial strain), steady (i.e. time‐invariant) structured shock waves within metal matrix composites…

Abstract

Purpose

Propagation of planar (i.e. one directional), longitudinal (i.e. uniaxial strain), steady (i.e. time‐invariant) structured shock waves within metal matrix composites (MMCs) is studied computationally. Waves of this type are typically generated during blast‐wave loading or ballistic impact and play a major role in the way blast/ballistic impact loads are introduced in, and applied to, a target structure. Hence, the knowledge of the basic physics of propagation of these waves is critical for designing structures with superior blast and impact protection capabilities. The purpose of this paper is to help advance the use of computational engineering analyses and simulations in the areas of design and application of the MMC protective structures.

Design/methodology/approach

To derive the overall response of the composite material to shock type loading, a dynamic‐mixture model is employed. Within this model, the known constitutive responses of the constituent materials are combined using the appropriate mixture rules. These mixture rules are of a dynamic character since they depend on the current state of the composite material and cannot be applied prior to the beginning of the analysis.

Findings

The approach is applied to a prototypical MMC consisting of an aluminum matrix and SiC particulates. Both the intermediate‐to‐strong shock regime (in which the contribution of stress deviators to the stress field can be ignored) and the weak shock regime (in which stress deviators provide a significant contribution to the stress field) are investigated. Finally, the computational results are compared with their experimental counterparts available in the open literature in order to validate the computational procedure employed.

Originality/value

Prediction of the spallation‐type failure in a metal‐matrix composite material (modeled using the dynamic‐mixture model) has not been done previously.

Details

Multidiscipline Modeling in Materials and Structures, vol. 7 no. 4
Type: Research Article
ISSN: 1573-6105

Keywords

Article
Publication date: 6 March 2009

A.M. Blokhin and R.S. Bushmanov

The purpose of this paper is to reply to the following question: do there exist piecewise smooth solutions to the 2D MEP hydrodynamical model of charge transport in…

Abstract

Purpose

The purpose of this paper is to reply to the following question: do there exist piecewise smooth solutions to the 2D MEP hydrodynamical model of charge transport in semiconductors with smooth parts separated by a surface of strong discontinuity?

Design/methodology/approach

A standard approach is used to obtain jump conditions for the balance equations under consideration.

Findings

For the balance equations of charge transport in semiconductors based on the maximum entropy principle Rankine‐Hugoniot jump conditions were derived and studied. Considering the important case of planar discontinuity, the authors discuss the legitimacy of the introduction of surface charge and surface current in the Rankine‐Hugoniot jump conditions.

Research limitations/implications

The jump conditions are derived for the balance equations written for the case of the parabolic approximation of energy bands. However, it is possible also to perform the analysis of corresponding jump conditions for the case of Kane dispersion relation approximation.

Originality/value

The paper presents derivation and study of Rankine‐Hugoniot jump conditions for the 2D MEP hydrodynamical model of charge transport in semiconductors.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 28 no. 2
Type: Research Article
ISSN: 0332-1649

Keywords

Article
Publication date: 10 October 2016

Mica Grujicic, Jennifer Snipes and S. Ramaswami

The purpose of this paper is to introduce and analyze a new blast-wave impact-mitigation concept using advanced computational methods and tools. The concept involves the…

Abstract

Purpose

The purpose of this paper is to introduce and analyze a new blast-wave impact-mitigation concept using advanced computational methods and tools. The concept involves the use of a protective structure consisting of bimolecular reactants displaying a number of critical characteristics, including: a high level of thermodynamic stability under ambient conditions (to ensure a long shelf-life of the protective structure); the capability to undergo fast/large-yield chemical reactions under blast-impact induced shock-loading conditions; large negative activation and reaction volumes to provide effective attenuation of the pressure-dominated shockwave stress field through the volumetric-energy storing effects; and a large activation energy for efficient energy dissipation. The case of a particular bimolecular chemical reaction involving polyvinyl pyridine and cyclohexyl chloride as reactants and polyvinyl pyridinium ionic salt as the reaction product is analyzed.

Design/methodology/approach

Direct simulations of single planar shockwave propagations through the reactive mixture are carried out, and the structure of the shock front examined, as a function of the occurrence of the chemical reaction. To properly capture the shockwave-induced initiation of the chemical reactions during an impact event, all the calculations carried out in the present work involved the use of all-atom molecular-level equilibrium and non-equilibrium reactive molecular-dynamics simulations. In other words, atomic bonding is not pre-assigned, but is rather determined dynamically and adaptively using the concepts of the bond order and atomic valence.

Findings

The results obtained clearly reveal that when the chemical reactions are allowed to take place at the shock front and in the shockwave, the resulting shock front undergoes a considerable level of dispersion. Consequently, the (conserved) linear momentum is transferred (during the interaction of the protective-structure borne shockwaves with the protected structure) to the protected structure over a longer time period, while the peak loading experienced by the protected structure is substantially reduced.

Originality/value

To the authors’ knowledge, the present work is the first attempt to simulate shock-induced chemical reactions at the molecular level, for purposes of blast-mitigation.

Details

Multidiscipline Modeling in Materials and Structures, vol. 12 no. 3
Type: Research Article
ISSN: 1573-6105

Keywords

Article
Publication date: 10 April 2017

Mica Grujicic, S. Ramaswami and Jennifer Snipes

In the recent work, a new blast-wave impact-mitigation concept involving the use of a protective structure consisting of bimolecular reactants (polyvinyl…

Abstract

Purpose

In the recent work, a new blast-wave impact-mitigation concept involving the use of a protective structure consisting of bimolecular reactants (polyvinyl pyridine+cyclohexyl chloride), capable of undergoing a chemical reaction (to form polyvinyl pyridinium ionic salt) under shockwave loading conditions, was investigated using all-atom reactive equilibrium and non-equilibrium molecular-dynamics analyses. The purpose of this paper is to reveal the beneficial shockwave dispersion/attenuation effects offered by the chemical reaction, direct simulations of a fully supported single planar shockwave propagating through the reactive mixture were carried out, and the structure of the shock front examined as a function of the extent of the chemical reaction (i.e. as a function of the strength of the incident shockwave). The results obtained clearly revealed that chemical reactions give rise to considerable broadening of the shockwave front. In the present work, the effect of chemical reactions and the structure of the shockwaves are investigated at the continuum level.

Design/methodology/approach

Specifically, the problem of the (conserved) linear-momentum accompanying the interaction of an incident shockwave with the protective-structure/protected-structure material interface has been investigated, within the steady-wave/structured-shock computational framework, in order to demonstrate and quantify an increase in the time period over which the momentum is transferred and a reduction in the peak loading experienced by the protected structure, both brought about by the occurrence of the chemical reaction (within the protective structure).

Findings

The results obtained clearly revealed the beneficial shock-mitigation effects offered by a protective structure capable of undergoing a chemical reaction under shock-loading conditions.

Originality/value

To the authors’ knowledge, the present manuscript is the first report dealing with a continuum-level analysis of the blast-mitigation potential of chemical reactions.

Details

International Journal of Structural Integrity, vol. 8 no. 2
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 28 September 2012

M. Grujicic, A. Arakere, B. Pandurangan, A. Grujicic, A. Littlestone and R. Barsoum

Polyurea falls into a category of elastomeric co‐polymers in which, due to the presence of strong hydrogen bonding, the microstructure is of a heterogeneous nature and…

Abstract

Purpose

Polyurea falls into a category of elastomeric co‐polymers in which, due to the presence of strong hydrogen bonding, the microstructure is of a heterogeneous nature and consists of a compliant/soft matrix and stiff/hard nanometer size hard domains. Recent investigations have shown that the use of polyurea as an external or internal coating/lining had substantially improved ballistic‐penetration resistance of metallic structures. The present work aims to use computational methods and tools in order to assess the shock‐mitigation ability of polyurea when used in the construction of different components (suspension‐pads, internal lining and external coating) of a combat helmet.

Design/methodology/approach

Shock‐mitigation capability of combat helmets has become an important functional requirement as shock‐ingress into the intra‐cranial cavity is known to be one of the main causes of traumatic brain injury (TBI). To assess the shock mitigation capability of polyurea, a combined Eulerian/Lagrangian fluid/solid transient non‐linear dynamics computational analysis of an air/helmet/head core sample is carried out and the temporal evolution of the axial stress and particle velocities (for different polyurea augmented helmet designs) are monitored.

Findings

The results obtained show that improvements in the shock‐mitigation performance of the helmet are obtained only in the case when polyurea is used as a helmet internal lining and that these improvements are relatively small. In addition, polyurea is found to slightly outperform conventional helmet foam, but only under relatively strong (greater than five atm) blastwave peak overpressures.

Originality/value

The present approach studies the effect of internal linings and external coatings on combat helmet blast mitigation performance.

Details

Multidiscipline Modeling in Materials and Structures, vol. 8 no. 3
Type: Research Article
ISSN: 1573-6105

Keywords

Article
Publication date: 10 August 2015

Mica Grujicic, Jennifer Snipes, Ramin Yavari, S. Ramaswami and Rohan Galgalikar

The purpose of this paper is to prevent their recession caused through chemical reaction with high-temperature water vapor, SiC-fiber/SiC-matrix ceramic-matrix composite…

Abstract

Purpose

The purpose of this paper is to prevent their recession caused through chemical reaction with high-temperature water vapor, SiC-fiber/SiC-matrix ceramic-matrix composite (CMC) components used in gas-turbine engines are commonly protected with so-called environmental barrier coatings (EBCs). EBCs typically consist of three layers: a top thermal and mechanical protection coat; an intermediate layer which provides environmental protection; and a bond coat which assures good EBC/CMC adhesion. The materials used in different layers and their thicknesses are selected in such a way that the coating performance is optimized for the gas-turbine component in question.

Design/methodology/approach

Gas-turbine engines, while in service, often tend to ingest various foreign objects of different sizes. Such objects, entrained within the gas flow, can be accelerated to velocities as high as 600 m/s and, on impact, cause substantial damage to the EBC and SiC/SiC CMC substrate, compromising the component integrity and service life. The problem of foreign object damage (FOD) is addressed in the present work computationally using a series of transient non-linear dynamics finite-element analyses. Before such analyses could be conducted, a major effort had to be invested toward developing, parameterizing and validating the constitutive models for all attendant materials.

Findings

The computed FOD results are compared with their experimental counterparts in order to validate the numerical methodology employed.

Originality/value

To the authors’ knowledge, the present work is the first reported study dealing with the computational analysis of the FOD sustained by CMCs protected with EBCs.

Details

Multidiscipline Modeling in Materials and Structures, vol. 11 no. 2
Type: Research Article
ISSN: 1573-6105

Keywords

Article
Publication date: 31 May 2011

Goran Ivetic

The aim of this paper is to give a simple and accurate tool for prediction and comparison of residual stresses in laser shock peened and shot peen treated materials.

Abstract

Purpose

The aim of this paper is to give a simple and accurate tool for prediction and comparison of residual stresses in laser shock peened and shot peen treated materials.

Design/methodology/approach

This work applies finite element code ABAQUS in order to compare the residual stress state and plastic deformation in specimens in aluminium alloy 7050‐T7451, treated with shot peening (SP) and laser shock peening (LSP) processes. Both processes are simulated using the Hugoniot elastic limit (HEL) of the material in question, and the processes are modelled using same input parameters (pressure on the surface of the specimen and the duration of contact between the material and the peening medium).

Findings

By using the same approach in both the analyses, a sound comparison of two technologies can be made, by comparing the obtained residual stress profiles. In addition, surface pressure and contact time can be varied easily in a parametric analysis, allowing the calibration of the numerical results.

Research limitations/implications

Owing to simplicity of used numerical models, different process parameters relative to SP process have not been taken in consideration directly, but through their effect on pressure on the surface of the specimen and the duration of contact between the material and the peening medium.

Originality/value

Application of HEL material model, usually applied to LSP problems, to the analysis of SP process gives promising results, in spite of simplicity of used numerical model.

Details

International Journal of Structural Integrity, vol. 2 no. 2
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 1 March 2007

M. Grujicic, B. Pandurangan, U. Zecevic, K.L. Koudela and B.A. Cheeseman

The ability of light‐weight all fiber‐reinforced polymer‐matrix composite armor and hybrid composite‐based armor hard‐faced with ceramic tiles to withstand the impact of a…

Abstract

The ability of light‐weight all fiber‐reinforced polymer‐matrix composite armor and hybrid composite‐based armor hard‐faced with ceramic tiles to withstand the impact of a non‐Armor‐ Piercing (non‐AP) and AP projectiles is investigated using a transient non‐linear dynamics computational analysis. The results obtained confirm experimental findings that the all‐composite armor, while being able to successfully defeat non‐AP threats, provides very little protection against AP projectiles. In the case of the hybrid armor, it is found that, at a fixed overall areal density of the armor, there is an optimal ratio of the ceramic‐to‐composite areal densities which is associated with a maximum ballistic armor performance against AP threats. The results obtained are rationalized using an analysis based on the shock/blast wave reflection and transmission behavior at the hard‐face/air, hard‐face/backing and backing/air interfaces, projectiles’ wear and erosion and the intrinsic properties of the constituent materials of the armor and the projectiles.

Details

Multidiscipline Modeling in Materials and Structures, vol. 3 no. 3
Type: Research Article
ISSN: 1573-6105

Keywords

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